Ion purification for plasma ion implantation

DETAILED DESCRIPTION In accordance with the present invention, ions in a plasma which are to be implanted in a target by the plasma source ion implantation process are purified to eliminate undesired ion species from the plasma before implantation.
The purification is carried out by an ion cyclotron resonance (ICR) technique in which the ions in the plasma are subjected to a time varying electric field in the presence of a steady magnetic field, which is selected to drive the unwanted ion species into resonance, and thus out to larger orbits, than the wanted species, and ultimately to drive the unwanted species into contact with a collection plate or other collection means where the unwanted species can be entirely removed from the plasma.
After the plasma has been purified, voltage pulses are applied to the target to implant the desired ion species into the target from the adjacent purified plasma.
A substantial decrease in the processing time required to implant ions over large surfaces may thus be obtained as compared with ion guns for semiconductor processing applications, and greater control of surface characteristics may be obtained in surface hardening or modification applications.
In addition, the equipment for carrying out implantation in accordance with the invention can be made compact so as to occupy much less floor space than conventional ion beam ion implantation equipment.
In the present invention, the ion plasma may be formed continuously and passed through a filter comprising an ICR system which drives out the unwanted species before the plasma is introduced into the plasma implantation region from which the ions in the plasma will be accelerated into the target.
A solenoidal magnet provides a constant magnetic field to an ion purification region in the ICR system.
Alternatively, the plasma may be generated adjacent the target in the plasma implantation region and may be purified in the intervals between the pulses of voltage applied to the target so that the plasma around the target is continuously purified